Using python decorator with or without parentheses

Question

In Python, what is the difference between using the same decorator with and without parentheses?

For example:

Without parentheses:

@some         


        

Answer 1

If you have a decorator that can be used with or without parameters, you can use the following decorator on your decorator to make it usable with or without parentheses, like this:

>>> @omittable_parentheses(allow_partial=True)
... def multiplier(multiply_by=2):
...     def decorator(func):
...         def multiplying_wrapper(*args, **kwargs):
...             return multiply_by * func(*args, **kwargs)
...         return multiplying_wrapper
...     return decorator
...
>>> @multiplier
... def no_parentheses():
...     return 2
...
>>> no_parentheses()
4
>>> @multiplier()
... def parentheses():
...     return 2
...
>>> parentheses()
4
>>> @multiplier(3)
... def parameter():
...     return 2
...
>>> parameter()
6

If allow_partial=True is given, the resulting decorator will also work with with partial:

>>> from functools import partial
>>> multiply_by_3 = partial(multiplier, multiply_by=3)
>>>
>>> @multiply_by_3
... def partial_no_parentheses():
...     return 2
...
>>> partial_no_parentheses()
6
>>> @multiply_by_3()
... def partial_parentheses():
...     return 2
...
>>> partial_parentheses()
6

Decorator code:

from functools import wraps

def omittable_parentheses(maybe_decorator=None, /, allow_partial=False):
    """A decorator for decorators that allows them to be used without parentheses"""
    def decorator(func):
        @wraps(decorator)
        def wrapper(*args, **kwargs):
            if len(args) == 1 and callable(args[0]):
                if allow_partial:
                    return func(**kwargs)(args[0])
                elif not kwargs:
                    return func()(args[0])
            return func(*args, **kwargs)
        return wrapper
    if maybe_decorator is None:
        return decorator
    else:
        return decorator(maybe_decorator)

As a bonus, this decorator decorator can be itself used with or without parentheses!